1. Field of the Invention
The present invention relates to a polishing apparatus, and more particularly to a polishing apparatus for polishing a surface of a workpiece such as a semiconductor substrate.
2. Description of the Related Art
More attempts are being made to use copper, which has a low electric resistivity and is highly resistant to electromigration, as a metal material for forming interconnections on a semiconductor substrate, rather than aluminum and aluminum alloys. Copper interconnections are generally formed by embedding copper in minute recesses defined in the surface of the semiconductor substrate. Chemical vapor deposition (CVD), sputtering, and plating processes are used to form copper interconnections. According to any of these processes, a copper film is deposited on the entire surface of the semiconductor substrate including a peripheral portion thereof while sealing the peripheral portion, and thereafter unwanted deposited copper is removed from the semiconductor substrate by chemical mechanical polishing (CMP). In this copper film growth process, when the sealing is incomplete, the copper film is deposited on a peripheral portion, i.e., an edge portion of the substrate, and a sputtered film of copper is attached to the reverse side of the substrate.
On the other hand, copper can easily be diffused into a silicon oxide film in a semiconductor fabrication process, impairing the electric insulation of the silicon oxide film. Thus, the remaining unnecessary copper needs to be completely removed from the substrate. Furthermore, the copper deposited upon film growth on the peripheral portion (edge portion and bevel portion) of the substrate other than the circuit area is unnecessary, and also may cause cross contamination in subsequent processes of delivering, storing, and processing the substrate. For these reasons, it is necessary that the remaining deposited copper on the peripheral portion of the substrate be completely removed immediately after the copper film growing process or the CMP process.
Defects and particles on the reverse side and bevel portion of the substrate may possibly cause microscratching in the CMP process, and dust attached to the reverse side of the substrate may drop onto a lower substrate in a carrier, causing defects on the lower substrate when a film is grown thereon. For these reasons, there is a growing need for the removal of defects and particles on the peripheral portion and reverse side of the substrate.
There have been made various attempts to remove copper defects from the peripheral portion and reverse side of a substrate. According to one attempt, while a substrate with a protective coating on the surface of a copper film deposited in the circuit area of the substrate is being rotated in a horizontal plane, a copper etching liquid is supplied to the peripheral portion of the substrate to dissolve and remove copper attached to the peripheral portion of the substrate. Another proposal is concerned with a process of immersing a substrate with a protective coating in an acid solution to etch away a metal film formed on the peripheral portion of the substrate. In still another approach, a silicon oxide film is formed on the surface of a substrate so as to entrap foreign matter and metal impurities, and then etched away from the surface of the substrate.
The above conventional processes of removing the unwanted deposits have an etching rate reduced depending on the types of film formed on the substrate, and cannot finish the etching process within a given period of time. If the temperature is raised to increase the etching rate in these conventional processes, then the equipment used becomes complex in structure for the need of increased resistance to chemicals and high temperatures.
The present invention has been made in view of the above drawbacks. It is therefore an object of the present invention to provide a polishing apparatus which has a compact structure and can effectively remove unwanted films and defects from a peripheral portion and reverse side of a substrate.
In order to achieve the above object, according to an aspect of the present invention, there is provided a polishing apparatus comprising: a feed reel for feeding a polishing tape wound thereon, the polishing tape having a polishing surface; a take-up reel for reeling up the polishing tape from the feed reel; a presser for pressing the polishing tape between the feed reel and the take-up reel against a surface, to be polished, of a workpiece; and a motor for rotating the take-up reel.
In this case, the presser may press the polishing tape against a side edge of the workpiece, or a reverse side of the workpiece, or a face side of the workpiece.
The polishing apparatus according to the present invention can effectively remove unwanted films and defects from the peripheral portion and reverse side of the workpiece, with a highly compact structure. The polishing apparatus can be used to polish not only the peripheral portion and reverse side of the workpiece, but also the face side (circuit area) of the workpiece such as a semiconductor substrate. In this case, the polishing apparatus can polish the face side of the substrate with more compact structure than a conventional CMP apparatus. Thus, the compactness of the polishing apparatus can be achieved.
According to a preferred aspect of the present invention, the polishing apparatus further comprises a cartridge housing the feed reel, the take-up reel, and the presser therein, and a cartridge holder for detachably holding the cartridge thereon.
According to another preferred aspect of the present invention, the polishing apparatus further comprises a cleaning unit for cleaning the polished surface of the workpiece and a drying unit for drying the workpiece which has been cleaned by the cleaning unit.
According to still another preferred aspect of the present invention, the polishing apparatus further comprises an inspection unit for inspecting the polished surface of the workpiece.
According to still another preferred aspect of the present invention, the polishing apparatus further comprises a vacuum chuck for holding the workpiece in such a state that a surface to be polished faces downwardly.
In this case, the vacuum chuck may comprise an annular vacuum seal on the peripheral portion thereof, and the vacuum seal may have a groove connected to a vacuum source.
According to still another preferred aspect of the present invention, the polishing apparatus further comprises a compression spring for biasing the presser toward the workpiece.
According to still another preferred aspect of the present invention, the presser comprises a bladder and a pressurized fluid supplied into the bladder.
The above and other objects, features, and advantages of the present invention will be apparent from the following description when taken in conjunction with the accompanying drawings which illustrates preferred embodiments of the present invention by way of example.